The present invention relates to an electronic leveling apparatus and a method of controlling the focusing operation of the electronic leveling apparatus. More particularly, the present invention relates to an electronic leveling apparatus or the like in which a pattern image of a staff received on a photoelectric converting unit is converted into an electric signal, a peak of contrast is detected based on the obtained electric signal, and thus focusing control is carried out.
A measurement of level difference is carried out by using a staff and a level measuring device. The staff is provided with a scale and numerical values indicating the height from the ground on which the staff stands. The level measuring device is arranged to collimate the horizontal direction.
The height of a target point is determined in such a manner that a benchmark point (a point of which height is given) or a known point is used as a reference and then level difference between the benchmark or the known point and the height of the target point is measured. To determine the height of the target point accurately, the distance between the surveying point to the target point is divided into sections of a predetermined length, the level measuring device is provided at the midst point of the section, and level difference is obtained by reading the scale of the staffs positioned in the front and rear direction of the level measuring device. This operation is repeated to measure the level difference.
When the level measuring device is utilized, the telescope is focused on the staff to collimate the scale of the staff. For this reason, the accuracy in reading the scale of the staff depends on the degree of skill of the operator. That is, the accuracy of measurement varies depending on the degree of skill of the operator. The electronic leveling apparatus is developed for the purpose of removing accuracy variation depending on the degree of skill of the operator and improving an efficiency of measurement.
Also, the electronic leveling apparatus is arranged as a level measuring device and utilized together with a staff. Since the electronic leveling apparatus reads the scale of the staff in an electronic manner, the electronic leveling apparatus is arranged to convert an optically sensed signal into an electric signal, convert the electric signal into a numerical digit and display the numerical digit on a display device. Since the numerical digit is memorized into a memory device directly, note taking or key input operation can be obviated.
The staff utilized together with the electronic leveling apparatus is substantially the same as the conventional staff. However, the staff is provided with a patterned scale and hence the scale can be read in an electronic manner. Thus, the scale cannot always be read by the surveyor. However, any operator can operate the measuring at a degree of skill equivalent to the skill of an expert so long as the operator has a certain knowledge. That is, the minimum requirement for the operator is that the operator directs the electronic leveling apparatus toward the staff and focuses the apparatus on the staff.
According to the conventional automatic focusing apparatus, due to an error caused in the assembly stage, humidity and temperature of surrounding atmosphere and so on, an optical distance can be fluctuated relative to a designed value. Alternatively, the focal position of a lens can vary. These fluctuation or variation will cause a positive or negative error in focusing amount (defocusing amount).
It is true that the conventional electronic leveling apparatus allows an operator to carry out surveying operation at a skill equivalent to the skill of an expert so long as the operator has a certain knowledge, and hence any problem can be removed by an electronic manner in terms of the reading of the scale on the staff. However, the conventional electronic leveling apparatus encounters a problem that an ordinary operator can achieve accuracy lower than accuracy which is achievable by an expert in terms of focusing operation. In other words, an accurate measuring operation requires that focusing adjustment shall be carried out while the main body of the electronic leveling apparatus is maintained in a horizontally collimated state.
The applicant of the present invention has developed an automatic focusing electronic leveling apparatus. However, the electronic leveling apparatus suffered from problems of focusing operation in terms of time and cost, and hence the developed automatic focusing electronic leveling apparatus cannot provide utility from a practical viewpoint.
Further, the conventional automatic focusing apparatus suffers from a problem of positive or negative error in the focusing amount that comes from the assembly stage, humidity and temperature of surrounding atmosphere and so on, with the result that an image cannot be formed on a photosensitive element. Thus, the focal position different from a theoretical focal position could be calculated in a wrong manner, which fact leads to a defocus state.
According to the present invention, there is provided an electronic leveling apparatus for use with a staff as a target of collimation having a pattern arrayed in the longitudinal direction thereof for determining level difference, in which a telescope optical system including a focusing optical system forms an image of the pattern, a photoelectric converting unit receives a light beam from the telescope optical system and converts the light beam into a signal of the pattern, a focusing drive unit forms the pattern on the photoelectric converting unit, and a focusing control unit detects a focusing status and controls the focusing drive unit based on the output signal of the photoelectric converting unit.